Hypertension Overview 9/10/2014 Flashcards
T/F: HTN is a disease
false: it is a syndrome that encompasses a large group of disorders
HTN is fundamentally a disorder of regulation of ________.
Systemic Vascular Resistance
HTN is believed to be the end product of the interaction of what 3 concepts?
-hereditary, environment, behavior
3 broad manifestations of HTN
- SAP is regulated at a sustained abnormally high level
- abnormal regulation of Na and body fluid metabolism
- abnormal fibrosis (deposition of collagen) in tissues
2 broad categories of hypertension
- primary (essential HTN) which can be resistance HTN or compliance hypertension (stiff pipes seen in old age)
- secondary HTN
3 big areas of detrimental consequences of HTN
- LV: generates a higher systolic P which increases LV wall stress in systole, causes LV hypertrophy (concentric), generalized fibrosis in myocardium that decreases LV diastolic compliance=impaired relaxation (diastolic dysfunction)
- arterial system: increase wall stress in SA system; arterial vascular disease (aneurysms, accelerates atherosclerosis), arteriolar disease: obliterative destruction which increases SVR even more
- Kidney: due to arteriolar destruction which further decreases ability to excrete Na
What is the most common cause of chronic renal failure?
-HTN causing obliteration of systemic arterioles including those in the kidney
4 main clinical consequences of HTN
- cardiac dysfunction due to progressive LVH and fibrosis: CHF
- accelerated atherosclerotic and aneurysmal disease of large-medium systemic arteries: MI, stroke, aneurysms increase
- progressive destruction of systemic arterials= increase SVR
- renal dysfunction secondary to renal destruction of arterioles: contributes to excess Na retention
Worldwide prevalence of HTN and the excess death rate people with it carry
- 1 billion people
- about 1% increase per year
CV morbidities associated with HTN
- CAD, Peripheral vascular disease, stroke, CHF
- all go up as severity of either systolic or diastolic HTN increases
Blood pressure and age
-thought to be normal that there is an age related increase with BP; systolic more so than diastolic and this means pulse pressure increases with age
Problems with the definition of hypertension
- epi: continuum of BP values in the population, disorder is so prevalent that it may appear normal, tendency for increase with age
- morbidity: continuum of frequency of morbidity with BP
When it comes to BP, ______ is always better!
-lower
Normal, preHTN, stage 1 and stage 2 HTN cut offs
Normal: / 160 or >/100
Primary vs Secondary HTN
primary: no identifiable cause linked to a particular organ system
secondary: caused by a disorder of 1 of the arterial pressure regulatory mechanisms: kidney disease, adrenal disease, CNS disease, drug intake
3 mechanisms which should prevent HTN but malfunction
- baroR reflex: reset to higher threshold
- pressure-natruiresis in kidney does not function appropriately
- RAAS: does not shut off renin as it should–some pts have ACE mutations
In what societies do we not see an increase in HTN prevalence with age?
-societies with low sodium diets–Yanomano Indians of SA
Impact of dietary sodium intake on HTN prevalence
- 1 tsp (<2 g/d is idea) but only 3.3% of world does this
- for each increase of salt intake (per g) BP increases more.
Dahl R and S rats and the significance
- R rats remained normotensive at high Na diet
- S rates developed severe HTN and died early on; had less renal Na output at any level of arterial inflow pressure
- impact of genetics
The Rice Diet
- diet virtually free of sodium fed to severely HTN patients
- produced dramatic reductions of BP with resolution of many abnormalities
- showed the beneficial effect of Na restriction
Factors other than Na intake known to influence prevalence of HTN
- environmental stress: HTN more prevalent in urban than rural pops; genetically predisposed individuals have a more pronounced vasoC response to stress than normals (seen in renovasculature)
2. obesity
3. physical inactivity: exercise reduces BP
4. alcohol consumption
Resistance vs Compliance HTN
- resistance: fundamental abnormalities is abnormal regulation of vascular resistance. SVR is elevated. Systolic, diastolic, and MAP are all elevated, pulse pressure is modestly elevated. Typical arterial P is 150/100
- compliance: issue = decreased great vessel compliance. SVR is normal or slightly elevated. Systolic P is elevated, diastolic is normal or low, MAP is modestly elevated. Pulse pressure is greatly elevated (due in part to inc pulse wave velocity). typical arterial pressure is 170/60
Consequences of compliance HTN
- severe LV P overload
- causes severe LVH (decreased LV diastolic compliance, causing diastolic HF– HFpEF)
- accelerated vascular disease: aortic aneurysms, Cerebrovascular dz
“Vicious Cycle” in HTN
- initial effects: increase total body Na, increase SVR
- subsequent effects: destroy systemic arterioles (inc SVR), lose functioning renal mass, tissue fibrosis (cannot excrete Na)
- consequences: progressive increase in SVR, progressive loss of renal function and ability to excrete Na, increase CV load (heart and arterial system), changes in LV systolic and diastolic properties
So what causes essential HTN?
- probably not a single disorder, or monogenic
- any explanatory mechanism must take into account heredity, environmental factors, Na relationship
Mechanism of essential HTN
- issue with too much Na that the kidney cannot excrete.
- this raises intraV blood volume and causes release of natriuretic hormone that inhibits the Na/K ATPase.
- this causes Na to build in cells which turns on the Na-Ca2+ exchanger which removes Na but increase intracellular Calcium–> vasoconstriction and increase SVR
What is Natriuretic Hormone?
-Not yet identified but believed to be a Na/K ATPase inhibitor important in developmental of essential HTN
Can anything be done in addition to picking a healthier, low Na diet?
Yes, weight loss amplifies these effects.
Renal Sympathetic Hyperactivity
- perhaps another possible mechanistic constributor to essential HTN
- pts with HTN have increase afferent and efferent renal sympathetic nerve activity
- denervation not seen to be better than sham
What is likely the fuel that drives the evolution of HTN in genetically susceptible individuals?
-dietary Na intake
